Nonaqueous electrolyte secondary batteries containing a positive electrode and a negative electrode, which allows lithium ions to be inserted and extracted, have been widely spread in various fields including electric automobiles, power storage systems and information devices as a battery having a high energy density. Accordingly, demands on such batteries have increased, and studies thereof have gathered pace.
In order to use the nonaqueous electrolyte secondary battery for a power source for an electric automobile, it is required that an energy density is high, i.e., a discharge capacity per unit weight or unit volume is large.
On the other hand, the safety becomes an issue as the discharge capacity per unit weight or unit volume becomes larger, and a secondary battery having a more excellent safety is required. One answer to solve the problem described above is an all solid secondary battery. The all solid secondary battery is a secondary battery using a solid electrolyte, literally, instead of a nonaqueous electrolyte, i.e., an organic electrolytic solution, which has been used up till now. The organic electrolytic solution is flammable, and thus technological developments to improve the safety when the organic electrolytic solution is used are energetically performed. Nevertheless, it is difficult to secure the sufficient safety. The all solid secondary battery needs not to use the organic electrolytic solution, and thus cannot be ignited in this case. Thus, the all solid secondary battery is a secondary battery having the very high safety.
However, since lithium ion conductivity of the all solid secondary battery tends to be lowered between a positive electrode and a negative electrode, an electrolytic solution may be used according to a configuration of a battery.